The present invention relates generally to heating apparatus and, in a preferred embodiment thereof, more particularly provides a fuel-fired, induced draft furnace having incorporated therein a vent overpressurization detection system for automatically deactivating the furnace burner(s) in the event that the furnace exhaust flue becomes restricted or blocked.
Many fuel-fired forced air residential heating furnaces utilize draft inducer fans to control the flow of burner combustion products through the furnace heat exchanger. In the typical arrangement, the draft inducer fan has an inlet connected to the heat exchanger outlet, and an outlet section connected to an external exhaust flue such that during furnace operation the draft inducer fan draws burner combustion products through the heat exchanger and discharges the combustion products into and through the external exhaust flue.
Safe operation of the furnace is dependant upon the draft inducer fan delivering the correct amount of combustion air to the furnace burners. If the draft inducer fan delivers an insufficient amount of combustion air to the burners, incomplete combustion will result, thereby causing the burner combustion products to contain unacceptably high levels of carbon monxoide. In the event that the external exhaust flue experiences an internal flow restriction or blockage, this unacceptably high carbon monoxide level in the burner combustion products readily occurs.
The conventional approach to preventing this potentially dangerous situation is to install an electric pressure sensing switch on the flue to continuously monitor the pressure created therein by the draft inducer fan. In the event that an unacceptably high pressure level within the exhaust flue is detected, indicating a restriction in or blockage of the flue, the pressure switch operates to deactivate the furnace burners so that the flue restriction or blockage may be appropriately removed, and the furnace returned to its normal, safe operation.
While the use of an electric pressure switch to detect flue restriction or blockage has proven to be a safe and effective solution to this problem, the incorporation of an electric pressure sensing switch in the typical residential furnace is relatively expensive.
It would accordingly be desirable to provide a vent overpressurization detection system which is less expensive. It is thus an object of the present invention to provide such a system.